Wireless communication networks, including network nodes and radio network device nodes such as cellphones and smartphones, are ubiquitous in many parts of the world. These networks continue to grow in capacity and sophistication. To accommodate both more users and a wider range of types of devices that may benefit from wireless communications, the technical standards governing the operation of wireless communication networks continue to evolve. The fourth generation (4G) of network standards has been deployed, and the fifth generation (5G, also known as New Radio, or NR) is in development.
Another development of modern wireless communication networks is support for expanded machine-to-machine (M2M) or machine type communications (MTC), variously known as the Networked Society or Internet of Things (IoT). This support is associated with new requirements on the networks, e.g., with respect to device cost, battery lifetime and coverage. To drive down device and module cost, using a system-on-a-chip (SoC) solution with integrated power amplifier (PA) is highly desirable. However, it is only feasible for the current state-of-the-art PA technology to allow ˜20-23 dBm transmit power when the PA is integrated to SoC. This constraint limits uplink “coverage,” which is related to the tolerable path loss between the radio network device and serving network node, such as a base station. To maximize the coverage achievable by an integrated PA, it is necessary to reduce PA backoff. PA backoff is needed when the communication signal has non-unity peak-to-average power ratio (PAPR). The higher the PAPR, the higher the PA backoff is needed. Higher PA backoff also gives rise to lower PA efficiency, and thus lower device battery life time. Thus, for wireless IoT technologies, designing an uplink communication signal that has as low PAPR as possible is critically important for achieving the performance objectives concerning device cost, battery lifetime, and coverage. Even for mobile broadband applications, it is desirable to have a technology that help the devices generate radio signals that have low PAPR.
Currently 3GPP is standardizing Narrow-band IoT (NB IoT) technologies. There is strong support from the existing LTE eco-system (vendors and operators) for evolving existing LTE specifications to include the desired NB IoT features. This is motivated by the time-to-market consideration, as an LTE-based NB IoT solution can be standardized and developed in a shorter time frame. A leading candidate for NB IoT, is a LTE based on a solution referred to as NB-LTE. LTE uplink however is based on single-carrier frequency-division multiple-access (SC-FDMA) modulation for the uplink data and control channels, and Zadoff-Chu sequences for random access.
Zadoff-Chu sequences have constant envelope. However, pulse shaping is needed to band limit their noise-like flat power spectral density before transmission. But the canonical LTE way of pulse shaping greatly destroys the constant envelope property of Zadoff-Chu sequence and the PAPRs of the resulting waveforms are relatively high.